


big sis

by WattStalf



Series: Commissions [125]
Category: Fire Emblem Series, Fire Emblem: Fuukasetsugetsu | Fire Emblem: Three Houses
Genre: Awkward First Times, Cunnilingus, F/M, Incest Play, Loss of Virginity, Vaginal Sex, commission
Language: English
Status: Completed
Published: 2020-06-14
Updated: 2020-06-14
Packaged: 2021-03-03 22:42:29
Rating: Explicit
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 1
Words: 4,012
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/24723238
Author URL: https://archiveofourown.org/users/WattStalf/pseuds/WattStalf
Summary: Caspar is a little dense, so Dorothea doesn't mind being a little straightforward with him, but when it comes to his biggest kink, it takes her a little effort to get him to be straightforward.
Relationships: Dorothea Arnault/Caspar von Bergliez
Series: Commissions [125]
Series URL: https://archiveofourown.org/series/1325462
Comments: 2
Kudos: 27





	big sis

**Author's Note:**

> this is literally canon, idk what y'all are on

As time goes by, as Dorothea and Caspar begin to grow closer, she can’t hope to deny her growing feelings for him. Especially after he shoots up in height, growing so suddenly and rapidly that he goes from simply adorable to overwhelmingly adorable  _ and _ incredibly hot on top of that. She knows that he wants her, and that will make it easier, now that she has figured out that she wants him. Though he can be a little dense at times, she is confident that she will be able to win him over in no time at all.

And, just as expected, he agrees to meet her in her room without issue, an old routine that the two of them had fallen out of. Perhaps he does not think anything of it at first, but once they are alone together, she knows that it will not be long before she has him giving her exactly what she wants. Dorothea locks the door behind her, while Caspar does not seem to notice, rambling on about something or other, and she goes over to join him, pretending to be interested in what he is talking about while waiting for the right chance to make her move.

She sits on her bed, and when there is a break in the conversation, she asks, “Don’t you want to sit down?”

“Oh, yeah, I guess,” Caspar replies, and goes to sit at her desk, only for Dorothea to stop him.

“Not over there!” she scolds him teasingly, before patting the spot next to her. “Come over and sit next to me, alright?”

He hesitates for a moment, and she can just imagine what must be going through his head, now that he has been invited to sit on a girl’s bed, right next to her, and she gives him a reassuring smile, letting him know that everything will be alright. With that, Caspar nods and goes to join her, sitting as far away from her as he can manage in such a small space. Naturally, Dorothea scoots closer to him, until their arms are brushing together, and he stiffens.

“Uh, so, where was I…?” He tries to lose himself in thought, but his eyes keep drifting over to her, distracting him from whatever topic he is trying to remember, making it impossible for her to forget where he actually is, or the fact that there is a gorgeous woman right next to him. His hands are on his knees, and she can see his knuckles whitening as he grips them, and so, she scoots even closer, laying her head on his shoulder.

“D-Dorothea?” he asks. “What are you...are you tired or something? Should I go? I can definitely go, if you don’t want me to...you know...I can…” He stammers, struggling to collect his thoughts, and not quite succeeding.

“Don’t be silly, Caspar. I invited you to my room for a reason, you know,” she murmurs, and he stiffens even more.

“Ya...ya did, huh? What reason might that be? Just to chat, right?” he asks. “Oh, or was it...it wasn’t more cleaning was it? If that’s the case, I should get up and get started!”

“It wasn’t for cleaning, don’t worry about that,” she replies. “Oh, and it wasn’t just to chat either. As fascinating as I may find that conversation, I had some other plans for you, actually.”

“But, then...I mean...what does laying on my shoulder have to do with that, exactly?”

“How dense can you possibly be?” she teases. “I wanted to be closer to you, of course!”

“Whoa, wait! You don’t mean that you...I mean, of course you don’t mean…” He trails off, laughing awkwardly and now, she is ready to make her move.

Turning her head, she stops his laughter short, pressing her lips to his, and he lets out a muffled noise of surprise as she kisses him. Dorothea throws her arms around his shoulders, turning her body so that she can properly hug him, and he remains stiff for so long that she is starting to wonder if she is going to have to do everything herself, but then she feels his hands, nervously touching the small of her back, and hesitantly, he begins to return her kiss.

Dorothea gives an enthusiastic moan to encourage him, but that just causes Caspar to stiffen up again, and she has to resist the urge to pull back and scold him. She knows that he is not trying to make this difficult, but it is still hard to believe that it takes this much effort to get him to give her what she needs. Still, she won’t give up when they have already made it this far, and she waits until he begins to relax again, holding her close.

Only then does she pull out of the kiss, pressing her forehead to his as she murmurs, “Do you understand what I invited you here for now?”

“I...I think so,” he mumbles, his eyes darting off to the side, though there is no way he can avoid her gaze right now. “But, you know...once upon a time, I kinda thought you were after this, and you definitely weren’t back then, so I thought...I mean…”

“A girl can change her mind, Caspar. Besides, that was back then, and this is now! You gave me time to get to know you, and that’s what made me interested,” she replies, giggling at the way his blush continues to deepen, the longer she stays close to him like this. “So? What do you say? Sounds good to you, doesn’t it?”

“I don’t know how I could be expected to say no,” he replies, and, after some hesitation, he looks straight forward again, matching her eye contact, trying to regain some of the confidence that he lost once she managed to knock him completely off-balance. He may not have any idea what he is doing, but that sure as hell is not going to stop him.

Dorothea pulls him into another kiss, pushing him back onto her bed as she does, and Caspar lets out a sharp noise of a surprise, muffled by her lips on his. She shifts her weight on top of him, so that she can feel just how excited he is right now, and she moans into his mouth, holding him down with her body.

When she breaks the kiss, she sits up, sitting back on him while he looks up at her, breathless and in awe, and Dorothea gives him a playful smile. She shifts her weight back so that she can maneuver out of her panties, letting them fall off the side of her bed, and says, “Before I let you have your fun, how about you help get me ready? And I can teach you a few things while we’re at it.”

“I don’t need you to teach me anything,” he lies quickly, though they both know he has no experience to speak of, and needs all the help that he can get.

“Come on, don’t you want to let your big sis help you out?” she teases, and he winces.

“Please don’t bring that up right now, it’s too weird,” he mumbles. Dorothea decides not to press the issue too much, because she has already teased him quite a bit, and she certainly doesn’t want to overwhelm him too much when this is only their first time. There will be plenty of time in the future for her to overwhelm him, but for now, she has her lessons to teach him, and despite him swearing that it is too weird to think of herself as his older sister, she finds that she still thinks along those lines, because she is serving as his loving guide, a mentor in the way she is certain a big sister would feel like. Well, besides the sexual matters, at least as far as most big sisters go.

Dorothea straddles his face, trying to walk him through what he needs to do for her, explaining things in such a way that she can imagine the way he must be blushing beneath her, as he assures her that he will be able to figure it out for himself as he goes. She tells him that there is no harm in her putting in the work to teach him, and he has to let her finish her explanation.

But by the end of it, she is so impatient that she can understand why he may have wanted to rush things along. Sitting on his face, she does what she can to take the lead even while he tries to follow her instructions, burying his tongue inside of her, and she tips her head back, moaning, perhaps a bit louder than she needs to, but she wants to encourage him, and wants him to feel like he is doing a good job. She wants him to know when he should continue, and what he should keep doing, until he is doing all that he can to please her, to leave her crying out for him as she rides his face.

She only does this for as long as she has to, and does not let herself get too close, before she pulls back, and gives him a chance to catch his breath. He mumbles, “Was i doing alright? Is you stopping a good sign or a bad one?”

“It means I’m finally going to give you what  _ you _ want,” she says, as she scoots back to straddle his lap. Quickly, she gets his pants out of the way. “You’ve done a good job so far, especially for your first time, so now we’re going to do what I actually invited you here for.”

His breath catches in his throat, and he nods, finding that he is unable to speak. Nodding is all he can do, as Dorothea rubs against the tip of his cock, causing him to whimper. He is more than ready for this, and she has done such a good job of teasing this out that she doubts he is going to last very long. It was a good call to indulge instead of merely getting ready for him, because he will not be able to do much for her this time, leaving everything in her hands for right now.

Slowly, she sinks down onto him, dragging this out as well, listening to the way that Caspar whimpers and groans, desperate for more that she will not give him just yet, taking her time as she fits him inside of her. She was ready for him, but even so, she takes things slow, giving him time to adjust to it, so that he won’t get too excited all at once. As it is now, it seems that he is just barely containing himself, whimpering and whining beneath her, until she has finally fit him entirely inside of her.

Then, she gives him a moment to catch his breath, shuddering beneath her, before she starts to rise and fall on top of him, earning more and more desperate, pathetic noises from him. Dorothea soon begins to lose herself in it as well, as she steadily picks up the pace, and the pleasure begins to take hold of her, until she can’t bring herself to drag it out anymore, bouncing on top of him and falling into a frantic and hungry rhythm as she does so.

Caspar groans and cries out for her, and she matches each moan with one of her own, working herself into a frenzy, until she is right on the edge. There is no more reason for her to hold back, so she doesn’t, letting her pleasure overtake her, until she is coming, and then, Caspar is helpless before this new sensation, joining her in her climax, whimpering for her and saying something that is hardly coherent.

It is only later, while really thinking about it, that she begins to suspect he was calling her, “Big sis.”

~X~

With that weighing on her mind after their first time together, Dorothea knows that she is going to have to find some way to confirm her suspicions. When she really thinks about it, it makes perfect sense that she might have managed to awaken something like that in him, what with all of the teasing, and even right before they actually fucked, she had teased him with it again. At the time, he had said it was weird, but, considering his little outburst at the end, that may have just been him trying to hide from her just how into it he really is.

If that is the case, then she can’t let something like this go. To her, the idea is incredibly exciting, and the more she thinks about Caspar playing the part of her little brother, the more excited she gets. Perhaps that is what drew her to him in the first place, even if she did not realize it at the start. His innocence and his stupidity- because there really is no nicer way for her to put it- make him the ideal little brother, and she had wanted to teach and guide him so much.

If he wants her to be his big sister, then she certainly won’t deny him that, and if he won’t admit to it on his own, then she can’t waste any more time with subtleties, nor can she count on the chance that he might slip up again. This is entirely up to her, and if she is going to get through to him, she already knows by now that she needs to be blunt about it.

Fortunately, getting him to come to her room again is not difficult after the first time, and now, he actually has an idea of what she wants from him. She spends some time kissing him and holding him close, making sure that the mood is properly set, wanting him to let his guard down before she goes in for the kill.

As Caspar pulls out of the kiss, he gazes at her with heavy-lidded eyes, an almost dreamy smile on his face, and she knows that now is as good a time as any. Returning his smile, she gently murmurs, “Now, Caspar, how would you like to call me your big sis again?”

All at once, he snaps out of it, going stiff while his eyes widen. “Wh...what was that?” he asks, even though she knows she spoke clearly enough that there is no way he did not hear her.

“I want you to call me your big sis again,” she replies, before casting her eyes down. “Judging by that... _ reaction _ , it seems like you want to do it too.” Looking back up, she watches as his face turns red, realizing that his erection has definitely given him away. He could blame it on the kiss, but she was pressed so close to him that she would have noticed a lot sooner.

Caspar knows that he is caught, and he tries to stammer a reply for a moment, only to fall silent soon after, knowing that he has no argument. Smirking, Dorothea pulls him into another kiss, and this time, she presses close enough to him to plainly feel his excitement, giving a few indulgent moans as she does. He must have really thought he got away with his outburst before, but now, she has him cornered with no escape.

Their clothes come off quickly after that, and soon enough, Dorothea is laying back on her bed, gesturing for Caspar to climb on top of her. “Since you did such a good job last time, your big sister is going to let you have a turn on top,” she coos, and his blush deepens as he comes over to join her.

“You really don’t have to talk to me like that, you know,” he mumbles, unable to look directly at her, and she laughs.

“Don’t be silly, little brother,” she replies. “Of course I do.”

His sigh is clearly put on, as he pretends to be exasperated to cover just how into it he is, but she knows that it will not be long before he is playing right into her hand. Caspar does not have the sort of resistance to stand a chance against her, after all.

“You remember what all you need to do, right?” she asks, and he scowls at her.

“Yeah, it’s not like it’s that…” He trails off, contemplating for a moment, before he asks, “Wait, do you need me to do...well, you know, the thing I did to warm you up before? We haven’t done anything like that yet.”

“There’s a good boy, I’m proud of my little bro for paying such good attention,” she praises him, and he glares off to the side, trying to fight a smile. “Things are going a little quicker this time, but that’s because I was expecting you, and had plenty of time to get ready on my own. Next time, I can teach you even more, but for now, I just want my good little brother to enjoy himself.”

Caspar only hesitates for a moment after that, likely debating whether or not it is worth it to protest what she says, but then, he must decide that it doesn’t matter at this point, because he begins to push down into her, groaning as he does. Dorothea relaxes beneath him, giving him little moans of encouragement as he fills her, reaching up to wrap her arms around his neck so that she can hold him close while he fucks her.

She can tell that he is trying to take things slow, whether for her sake or his own, but that it is difficult for him, and difficult not to let his excitement get the better of him. He is throbbing with his need, and struggling against that must not be easy for him, so of course, she has to praise him for his efforts yet again.

“So good,” she murmurs, and he gives a flustered little grumble, likely wanting to protest her praise further, but rendered otherwise speechless. “That’s my good little brother.”

Of course, hearing something like that from her lips is too much for him to hold back against, even when he wants to pretend that he is not as into it as she thinks he is. His slow pace suddenly speeds up, as he whimpers, thrusting into her and nearly losing himself in it, before he manages to snap out of it, slowing down again. Though she is glad that he managed to regain his self-control, because she would like to enjoy this for as long as possible, she knows that it will not be long before she pushes him over that edge again, because she simply can’t resist pushing his buttons, not when his reactions are so adorably predictable.

Dorothea wraps her legs around him, allowing him to sink deeper into her, filling her as he cries out, desperate and pathetic, and all hers. Clinging to him, she murmurs more and more praise between moans, letting him work his hips on top of her, struggling to keep it to a steady pace, struggling to not give into his desires and go too far, too quickly. She lets him steady himself, lets him find a pace that works for him, and lets him start to relax into it, before she starts to push at him again.

“My good little bro,” she coos, and is immediately met with harder thrusts and a quicker pace, Caspar grunting and biting his lip, losing himself right away. He struggles to reign himself back in, just as soon as he realizes just how easily he is getting carried away, but she repeats herself, telling him just how good he is, and he just can’t help himself.

“St-stop…” he finally whimpers, after struggling for some time to catch his breath and remember just how to speak. “You’re too...that’s too…”

“Too much?” she breathes. “You just mean that you like it too much, though. It’s okay, little bro, I’ve already got you all figured out.”

Caspar gasps and moans, his body moving as if on its own, compelled to keep fucking her harder, even when he knows that, if he wants to try and prove his point to her, that he must show restraint. There is just no way for him to prove that point, because they both know the truth, and both know what it is that he wants. All he has to do is admit to it, to really give in to her, and she will always be able to give that to him, whenever he wants it, because she wants it just as badly as he does. From the start, this is what she has wanted, even when she did not quite realize it yet.

“My good,  _ good _ little brother...won’t you tell your big sis how much you love it?” she asks him, and he stiffens, visibly wincing, the battle clear on his face. He wants to do as she says just as much as he does not want to give her the satisfaction, and no matter how he may try to fight the part of him that wants the former, he is going to give in sooner or later, especially with Dorothea continuing to egg him on. “Come on, I want to hear you say it...tell your big sis, please?”

“I-I love it!” he cries out at last, but he hesitates, not saying the most important thing. “I love it…”

“Come on, little bro...you love it...who? You can say it, there’s nobody here but us,” she encourages him, and he groans and gasps and thrusts harder and faster, perhaps trying to distract her from it or maybe trying to distract himself, or maybe just so overwhelmed that it is all he can think to do.

Whatever the case, there is nothing he can do to fight her, not when she has him like this, and as she clings to him, begging for him to say it, the part of him that wants it and does not give a damn about his pride finally wins out. “I love it, big sis!” he cries, sounding so needy that she is suddenly even more determined to take care of him, even more determined to be the big sister that he needs.

“You do?” she murmurs, her own voice starting to give way to moans. He is fucking her so hard now that it is a wonder she can speak to him at all, and she is right on the edge, needing just one final push to send her over it. “Oh, please, say it again, little brother!”

“I love it!” he replies, before correcting herself, and telling her exactly what she wants to hear. “I love  _ you _ , big sis!”

As she comes, she cries out and is hardly coherent, but she at least manages to reply, “Oh, I-I love you...my little brother!” She only hopes that that is coherent enough for him to understand, but then, he is right there with her, whimpering and calling out to his big sister as he comes as well.

Caspar soon goes limp on top of her, exhausted and overwhelmed, and as Dorothea catches her breath, she begins running her fingers through his hair, patting him on the head to let him know that he has done a very good job. It might have taken him some getting used to, but she just knew that, if she made him actually admit to it, that he would love every second of it.

And now, neither of them will ever have to hide from this side of themselves ever again. As long as they are alone together, he can play the part of her needy little brother, while she plays the part of the big sister that he has always needed.

**Author's Note:**

> If you're interested in my writing updates, please follow my fanfiction twitter @WattStalf  
> 


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